Scientists had earlier believed that the Mariana Trench and the Kermadec Trench of the Pacific Ocean were insulated from human influences because they happen to be the deepest parts of the ocean at over 10 kilometers deep and at a distance of 7,000 kilometers apart from each other. But this assumption has now been shattered by a new study published on Monday in the journal Nature Ecology and Evolution.

From the published study, researchers from the University of Aberdeen and the James Hutton Institute in the UK found that concentrations of chemical pollutants are far more palpable in the deepest parts of the world's oceans largely uninhabited than earlier thought. The research team was led by Dr. Alan Jamieson of the University of Newcastle.

Banned chemical substances dominate the depths of the seas

The researchers found that both the Mariana and Kermadec trenches were full of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) - two chemicals banned by the US in 1979 and the Stockholm Convention on Persistent Organic Pollutants in 2001. Both PCBs and PBDEs were frequently used in the production of fire extinguishers and electrical insulators, the BBC reports.

Scientists discovered that these two banned chemicals among others do not break down or degrade in the environment, so they ultimately find their ways into the waters where marine creatures absorb them. The two chemicals also flow into waters via landfill discharges and industrial accidents, finally settling in the depths of the oceans where they cause havoc to marine ecosystems.

Plastic debris littering the oceans also contains these chemicals and when fish consume these plastics, they become tainted with the pollutants. Dead fish or other marine creatures tainted with the chemicals may die and sink to the ocean floor where other deepwater creatures consume them as well, and the entire food chain becomes contaminated with the banned substances, the Washington Post explained.

Deepwater amphipods were tainted with the contaminants

Deepwater shrimp-like crustaceans known as amphipods inhabiting the depths of the Mariana and Kermadec trenches were found to be contaminated with both PCBs and PBDEs. The fact that amphipods living 10 kilometers below the sea surface where other marine creatures cannot survive become contaminated with these chemicals indicate the level to which other marine creatures living closer to the surface of the ocean would have been infected with these pollutants. These chemicals are also capable of poisoning humans as well.

Katherine Dafforn, a marine ecologist with the University of New South Wales, made this clearer by pointing out that study authors "have provided clear evidence that the deep ocean, rather than being remote, is highly connected to surface waters and has been exposed to significant concentrations of human-made pollutants."